Conventionally, there are ones disclosed in Patent Documents 1, 2 and 3 as illustrated in FIGS. 21 to 24. FIG. 21 is a front main part view illustrating a state of a stator core attached to a core case by shrink-fitting. FIG. 22 is a front main part view illustrating the stator core. FIG. 23 is a front main part view illustrating a state of a stator core attached to a core case by shrink-fitting. FIG. 24 is a sectional view illustrating a state of a stator core attached to a core case by shrink-fitting.
In all FIGS. 21 to 24, stator core segments 103A, 103B and 103C of stator cores 101A, 101B and 101C of motors are joined to form an annular shape and are received and fixed by shrink-fitting in core cases 105A, 105B and 105C.
Where, there is a problem that iron loss increases due to compressive stress generated in the stator core segments 103A, 103B or 103C at the time of the shrink-fitting so that output efficiency of a motor comes down.
To address this, the stator core 101A of FIGS. 21 and 22 has slits 101Aa made therein so as not to generate compressive stress, and the stator cores 10B and 103C of FIGS. 22 and 24 have holes 103Ba and 103Ba to reduce compressive stress.
However, the slits 101Aa and the holes 103Ba and 103Ca make an increase of magnetic resistance and result in a problem of deteriorating magnetic properties.
On the other hand, in the case of the slits 101Aa, it is conceivable to compressively deform contacting portions on the outer peripheral side toward a direction to eliminate the slits (circumferential direction) by the compressive stress.
However, only the deformation amount due to the distortion around the contacting portions on the outer peripheral side results in the small amount of the compressive deformation of the contacting portions, and it is physically difficult to eliminate the slit 101Aa.
Such a problem also exists in stator cores other than a divided-type stator core.    Patent Document 1: JP 2005-51941 A    Patent Document 2: JP 2009-261162 A    Patent Document 3: JP 2002-136013 A